As a conventional estimating method of the remaining capacity of a battery (that is, an estimating method of the charging state of a battery), there is generally known a method in which a battery terminal open-circuit voltage is made as an initial value of the charging state (SOC: State of Charge) of the battery, and a correction is made using an integration value of battery charging/discharging current.
Besides, JP-A-2001-174535 (FIG. 1 and paragraph 0039) discloses “a battery capacity arithmetic operation device in consideration of polarization” in which an accurate I-V (current-voltage) approximate straight line in consideration of polarization of a battery is obtained, so that the charging state with high accuracy can be obtained even in a hybrid car.
In the battery capacity arithmetic operation device in consideration of polarization disclosed in JP-A-2001-174535, it is disclosed that voltage and current of a battery to cause a discharge current to flow through a load of a vehicle is collected to obtain a voltage-current characteristic, the current voltage of the battery is estimated by using the voltage-current characteristic, and the current charging state of the battery is obtained from this estimated voltage, while a battery voltage at a time after the collected current first reaches a large current at the occurrence of maximum polarization of the battery and when the current first reaches a specified current value not larger than the large current after the arrival, is made as an estimated voltage at a maximum polarization influence remaining time in a state where the influence of the maximum polarization remains, and the charging state is corrected by using a difference between the estimated voltage at the maximum polarity influence remaining time and an open-circuit voltage of the battery at the start of driving. However, since the open-circuit voltage of the battery is greatly influenced by the charging, and discharging history up to that time, about one day is required before it becomes stable, and when the charging state during driving is corrected on the basis of the open-circuit voltage immediately before the driving, a judgment error of the charging state can become large.
For example, in such an idling stop vehicle which attracts lots of attention in recent years and has an object to achieve low emission gas and low fuel consumption, since a function to make an engine stop during idling is provided, it is necessary for the battery to store electric power capable of restarting the engine after the engine is stopped, and it is necessary to accurately grasp the charging state (that is, the remaining capacity of the battery) during the use of the battery.
However, since the open-circuit voltage of the battery and the battery capacity are changed due to the influence of amount of battery electrolyte, degradation (softening, corrosion, sulfation, etc.), battery temperature, polarization, and the like, it has been difficult to accurately estimate the battery remaining capacity.
Besides, there are various combinations of a battery size and a performance rank with respect to an automobile rank of an idling stop vehicle determined from an engine displacement and a starter motor or a motor generator and a consumed electric current (hereinafter referred to as an application to be applied) during idling stop of the vehicle.
When this combination is changed, since the remaining capacity of the battery necessary for outputting a battery-minimum output required by the application to be applied is changed, it has been conventionally necessary to review a charging state monitor device corresponding to the application each time the application to be applied is changed.